1. Field of the Invention
The invention relates to a polymeric coated diffuse light reflector for use in light reflective articles such as lighting fixtures and the like in which diffuse light reflectance is desired, and specifically to polymeric coated diffuse light reflectors with an opaque blackout layer.
2. Description of Related Art
Reflectors are used in numerous types of lighting fixtures to maximize the usable light, thus increasing the lighting efficiency. Maximization is achieved through a combination of reflecting and redirecting light generated by the lamp in a desired direction, and minimizing the light absorbed by the reflector. This is particularly important when the light fixture design includes a light cavity in which light rays are redirected multiple times within the cavity before exiting the light fixture as usable light. Fixtures that use reflectors include tubular fluorescent lamps and light emitting diodes (LED).
Tubular fluorescent lamps emit light in 360 degrees around the lamp, thus the reflector redirects light from the back of the lighting fixture as usable light. LED light fixtures use a reflector in order to mix, obscure, or diffuse the discrete image(s) of individual LED lamps. This reflector often consists of painted metal or highly polished aluminum. It is desirable to maximize the light reflected by the reflector and minimize the light absorbed by the reflector, as any light absorbed is unusable, thereby decreasing the efficiency of the fixture.
Additionally, reflectors are used in horticulture applications to distribute and maximize light in a grow space environment. Because natural and man-made source of light, such as LED, HID (High Intensity Discharge) and tubular fluorescent lamps are emitting light from relatively fixed position(s), the distribution of light is unevenly dispersed from the canopy down to the stem/trunk of the subject plant. Gardeners employ reflectors in the grow space environment to redirect this light back onto the subject plant. Distributing light on the sides and underneath the foliage of the plant helps the overall stimulation of the subject and encourages healthy foliage/fruit growth. Having light reflected underneath the leaves is also know to discourage molds, fungi, and pests.
Diffuse reflectance occurs when incident light is reflected by a surface such that the reflected light is scattered randomly or in a Lambertian fashion. By contrast, specular reflectance occurs when incident light is reflected at the same angle as the incident angle. Specular reflectors have been used in light fixtures to both direct light out of the fixture in a controlled or focused distribution and increase overall fixture efficiency. Diffuse reflectance is preferred in situations in which low glare is desired and/or in which it is desired to distribute light evenly over as broad an area as possible. White, diffuse reflectors are often used in room and office lighting to reduce specular glare.
The reflector surface includes metal components fabricated from coil steel or aluminum. Coil steel or aluminum is coated in continuous coil equipment with a paint typically containing titanium dioxide light scattering particles, and the coating is subsequently cured. The resulting coil surface has a reflectance of up to about 91% and can be metal-formed into reflectors or light fixture bodies. Alternatively, powder coat paint is applied to light fixtures post metal-forming to provide a surface reflectance of up to 94%.
Plexifilamentary film-fibril sheet material made by flash spinning high density polyethylene sold under the trade name DuPont™ Tyvek® is known for use as a light reflective material. Such sheet material is believed to have a high diffuse reflectance because it is made from continuous fibers having a refractive index of 1.4 and because it contains voids or pores having an average diameter of less than 600 nm. Such sheet material may be preferred over many other known polymer-based sheet materials used in light reflectors because of the relatively high degree of diffuse reflectance and its color stability in the presence of ultraviolet light.
Other known sheet or roll-good plastic based white reflectors include multilayer PET films filled with titanium dioxide (TiO2) or barium sulfate then bi-axially stretched to create microvoids conducive to light reflection, such as Lumirror® film available from Toray Plastics (America), Inc. (North Kingstown, R.I.). Another known reflector material is a reflective microcellular foamed polymer sheet, such as reflective microcellular foamed polyester sheet available as MC-PET from Furukawa Electric Co. Ltd. (Tokyo, Japan). Another known reflector material is a highly reflective film made by expanding polytetrafluoroethylene (ePTFE) to create inter-tangled fibrils with voids that reflect light, such as those available from W. L. Gore & Associates, Inc. (Newark, Del.).
In light fixture fabrication for fluorescent office or general lighting fixtures, coil steel or aluminum is typically used as the fixture housing and possibly also as the reflector placed behind the lamp. The housing and/or reflector metal strips are stamped or roll-formed from a pre-painted metal sheet or coil. Stamping is done with a single or progressive die for more demanding dimensional changes. Other metal forming metal operations may include punching to form wire access holes or knock-outs, bending or computer-controlled cutting. Coil paint formulations are designed to withstand the many possible metal forming operations without cracking, crazing or delaminating.
Housings are used to secure the lamp, ballast connections, and may serve as the reflective surface behind the lamp. In many cases a metal reflector is placed in the housing behind the lamp to improve light output. Anodized specular aluminum reflectors are common for this use along with high reflectance painted white aluminum.
Forming a metal-plexifilamentary film-fibril sheet laminate is limited by the surface properties of the plexifilamentary film-fibril sheet. The porous nature of the sheet makes it susceptible to contamination from machine oil present in the forming process. The fibrous nature of the material presents an aesthetically different surface than paint and also can lead to fraying on punched or cut edges.